OSI stands for Open System Interconnection Reference Model. It divides network architecture into seven different layers. A layer is a collection of conceptually similar functions that provide services to the layer above it, and receives services from the layer below. The seven layers are shown in the diagram below.

Layer 7 – The Application Layer

This layer interacts with the end user. It provides network services to the user’s applications. Unlike other layers in the OSI model layer 7 does not provide services to any other OSI layer. Authentication services run at this layer. The application layer establishes the availability of the remote communication partner, and ensures that both ends agree on procedures for error recovery, privacy and control of data integrity.

Common protocols and services that run at layer 7 are SMTP, POP3, Telnet, HTTP, FTP and SNMP.

Firewalls also run at layer 7.

Layer 6 – The Presentation Layer

The presentation layer properly formats the data and ensures that the information the application layer sends out on one system is readable by the application layer of another system. An example of a presentation layer issue is when you open a document in word and there are lots of unrecognisable characters. The presentation layer is concerned with:

• Compatibility with the operating system.
• Proper encapsulation of data for network transmission.
• Data formatting (ASCII, Binary).
• Data encryption, compression, and translation.

Some of the file types that are used at the presentation layer are JPEG, ASCII, GIF etc..

Layer 5 – The Session Layer

The session layer establishes, manages, and terminates sessions between two communicating hosts. It provides its services to the presentation layer. The overall communication between two hosts is referred to as a session. As an example a web server might have a number of users, so many communication processes are open at a given time. Therefore, keeping track of which user communicates on which path is important.

Layer 4 – The Transport Layer

The transport layer segments data from the sending host and ensures that when the data gets to the destination host that it is in the correct order and free of errors. TCP which is connection-oriented and UDP which is connectionless reside at this layer.

Layer 3 – The Network Layer

The network layer provides connectivity and path selection (routing) between two host systems that might be located on geographically separated networks. IP addressing runs at this layer.

Layer 2 – The Data Link Layer

Most Switches, bridges and wireless access points run at this layer. Devices such as cable & DSL modems also run at layer 2. Other specifications that run at layer 2 are:

• Ethernet
• High Data Link Control (HDLC)
• Point-to –point Protocol (PPP)
• Frame Relay

Ethernet MAC addresses are at this layer. Layer 2 performs error detection using FCS (Frame Check Sequence) but this layer does not perform error recovery.

Layer 1 – The Physical Layer

The physical layer handles the actual data transmission. Characteristics such as voltage levels, timing of voltage changes, physical data rates, maximum transmission distances, physical connectors and cables are defined by physical layer specifications.

File conversions

Newer versions of the software can open older versions of the files but what do you do if you have an older version of AutoCAD?

You can always go back to the person that sent you the file and ask them to save it to an earlier version for you (although an easier method is to use DWG Trueview!). In AutoCAD if you go to  Save As in the Files of type drop down you can select the DWG version.

To set the default file version, open up the AutoCAD options and under the Open and Save tab you can set the DWG version that you want to save all files in.

DWG Trueview

DWG Trueview allows you to batch convert DWG files to a different version its also available from Autodesk for free! You can download it here http://usa.autodesk.com/adsk/servlet/pc/index?id=6703438&siteID=123112

Open DWG Trueview and select DWG Convert.

You can then select the files that you want to convert and the DWG version that you want to convert to.

DWG Trueview allows you to add your own conversion setups as well so you could save down as low as AutoCAD LT97. There is also an option to Purge and Audit each drawing!

The first thing we need to do is configure the VTP mode. There are three different modes available when configuring VTP

• Server – VLANs can be created deleted or modified VLAN configurations are stored in NVRAM
• Client – VLANs cant be created deleted or modified
• Transparent – VLANs can be created deleted or modified but VLAN information received from other switches within the network is ignored

In a large environment you should have two switches configured as VTP servers for redundancy. Start by logging into the switch and enter global configuration mode then change the VTP mode to Server as shown below (the default mode on a switch is server so this step might not be nessessary).

Now we need to configure the VTP domain by using the following command. Note that the domain name is case-sensitve.

The next step is to configure a password for the VTP configuration this is also case-sensitive.

The next step is optional. VTP pruning reduces network bandwidth by reducing unnecessary flooded traffic.

The above will configure a VTP server, if you want to configure a VTP client you can use the steps below

VLANs allow you to do the following:

• Group common network devices together and protect them by segregating them from other VLANs
• Segment devices into smaller LANs creating smaller broadcast domains
• Reduce the workload of Spanning Tree Protocol (STP) by limiting a VLAN to a single access switch
• To separate traffic sent from IP phones and PCs

Without VLANs a switch considers all of its interfaces to be in the same broadcast domain, by default all interfaces are assigned to VLAN 1 this can be seen by running the following command on the switch

As you can see from the output above all of the ports are in VLAN1 and the name for this VLAN is default.

To put switch ports into separate VLANS you need to begin by making the ports access ports by using the command below in interface configuration mode.

The next command puts the port into the VLAN that you want

Note that the message states that VLAN 13 did not exist and has now been created. For this scenario I went and added the corresponding ports to the correct VLANs using the commands above making sure I put ports 2 and 4 into VLAN 24 my switch is now set up as shown below.

Please note that now we have two separate VLANs hosts 1 & 3 cant communicate with hosts 2 & 4 and vice versa. They can only communicate through a layer 3 device such as a router or a layer 3 switch. There is also a technique called Router on a Stick which I have discussed in another post.

The packet tracer file for this secnario can be downloaded below.

Cisco VLANs

01: SW0#show interfaces fastEthernet 0/1
02: FastEthernet0/1 is up, line protocol is up (connected)
03:   Hardware is Lance, address is 0060.3e6b.0501 (bia 0060.3e6b.0501)
04:  BW 100000 Kbit, DLY 1000 usec,
05:      reliability 255/255, txload 1/255, rxload 1/255
06:   Encapsulation ARPA, loopback not set
07:   Keepalive set (10 sec)
08:   Full-duplex, 100Mb/s
09:   input flow-control is off, output flow-control is off
10:   ARP type: ARPA, ARP Timeout 04:00:00
11:   Last input 00:00:08, output 00:00:05, output hang never
12:   Last clearing of "show interface" counters never
13:   Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
14:   Queueing strategy: fifo
15:   Output queue :0/40 (size/max)
16:   5 minute input rate 0 bits/sec, 0 packets/sec
17:   5 minute output rate 0 bits/sec, 0 packets/sec
18:      956 packets input, 193351 bytes, 0 no buffer
19:      Received 956 broadcasts, 0 runts, 0 giants, 0 throttles
20:      0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
21:      0 watchdog, 0 multicast, 0 pause input
22:      0 input packets with dribble condition detected
23:      2357 packets output, 263570 bytes, 0 underruns
24:      0 output errors, 0 collisions, 10 interface resets
25:      0 babbles, 0 late collision, 0 deferred
26:      0 lost carrier, 0 no carrier
27:      0 output buffer failures, 0 output buffers swapped out

01: SW0#show interfaces fastEthernet 0/1

02: FastEthernet0/1 is up, line protocol is up (connected)

FastEthernet0/1 is administratively down, line protocol is down (disabled)

FastEthernet0/1 is down, line protocol is down (disabled)

03: Hardware is Lance, address is 0060.3e6b.0501 (bia 0060.3e6b.0501)

Hardware is Lance, address is 0060.3e6b.0502 (bia 0060.3e6b.0502)

SW0#conf tEnter configuration commands, one per line.  End with CNTL/Z.
SW0(config)#int fa0/1
SW0(config-if)#mac-address 0000.0000.0001

04: BW 100000 Kbit, DLY 1000 usec,

05: reliability 255/255, txload 1/255, rxload 1/255

06: Encapsulation ARPA, loopback not set

07: Keepalive set (10 sec)

08: Full-duplex, 100Mb/s

09: input flow-control is off, output flow-control is off

10: ARP type: ARPA, ARP Timeout 04:00:00

11: Last input 00:00:08, output 00:00:05, output hang never

12: Last clearing of "show interface" counters never

13: Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0

14: Queueing strategy: fifo

15: Output queue :0/40 (size/max)

16: 5 minute input rate 0 bits/sec, 0 packets/sec

17: 5 minute output rate 0 bits/sec, 0 packets/sec

18: 956 packets input, 193351 bytes, 0 no buffer

19: Received 956 broadcasts, 0 runts, 0 giants, 0 throttles

20: 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort

21: 0 watchdog, 0 multicast, 0 pause input

22: 0 input packets with dribble condition detected

23: 2357 packets output, 263570 bytes, 0 underruns

24: 0 output errors, 0 collisions, 10 interface resets

25: 0 babbles, 0 late collision, 0 deferred

26: 0 lost carrier, 0 no carrier

27: 0 output buffer failures, 0 output buffers swapped out

To begin with install Windows 2008 without activating it by running the setup and when prompted for an activation key do not enter anything and then click No to the message that appears. The 60 day trial period begins when the setup process has finished. Microsoft provide a script that can tell you how long you have left before your activation period expires to run the script open a command prompt and type the following slmgr.vbs –dli you might have to wait a moment while the script runs.

You will then see a dialog box showing you the time remaining until activation is required.

To extend your activation period for a further 60 days you can use the same script but with the –rearm switch as shown below (only do this when your first 6-0 day activation period is nearly finished though!)

Microsoft has an XML code example on their site available here http://support.microsoft.com/default.aspx/kb/948472 that can be used with task scheduler to make this process happen automatically.

• The 32 bit version supports a maximum of 4Gb of RAM and up to Four processors in a Symmetric Multi-Processing (SMP) configuration.
• The 64 bit version supports a maximum of 32Gb of RAM and up to Four processors in a Symmetric Multi-Processing (SMP) configuration.
• This edition supports NLB (Network Load Balancing) but does not support failover clustering.

Windows Server 2008 Enterprise Edition

• The 32 bit version supports a maximum of 64Gb of RAM and up to Eight processors in a Symmetric Multi-Processing (SMP) configuration.
• The 64 bit version supports a maximum of 2Tb of RAM and up to Eight processors in a Symmetric Multi-Processing (SMP) configuration.
• Support for failover clustering.
• Support for Active Directory Federation Services.

Windows Server 2008 Datacenter Edition

• The 32 bit version supports a maximum of 64Gb of RAM and up to Thirty Two processors in a Symmetric Multi-Processing (SMP) configuration.
• The 64 bit version supports a maximum of 2Tb of RAM and up to Sixty Four processors in a Symmetric Multi-Processing (SMP) configuration. 
• Support for failover clustering.
• Support for Active Directory Federation Services.
• Unlimited virtual image rights.

Windows Server 2008 Web Edition

• The 32 bit version supports a maximum of 4Gb of RAM and up to Four processors in a Symmetric Multi-Processing (SMP) configuration.
• The 64 bit version supports a maximum of 32Gb of RAM and up to Four processors in a Symmetric Multi-Processing (SMP) configuration.
• Support for NLB (network Load Balancing) clusters

Windows Server 2008 for Itanium-Based Systems

• Supports a maximum of 2Tb of RAM and up to Sixty Four processors in a Symmetric Multi-Processing (SMP) configuration.

The editions above are available in a Server Core edition. The server core edition is a stripped down version of Windows Server 2008 and is administered from a Command Shell.

The display of these control polygons can be turned on and off by using these keyins.

SET INVISGEOM NEVER – will turn off the display of invisible geometry.

SET INVISGEOM ALWAYS – Will turn on the display of invisible geometry.

SET INVISGEOM BYELEMENT – Allows you to set the display of the control polygons depending on if they have  been specifically turned on for a particualr element. If you select an element in your drawing and then use the element information tool control polygons can be turned on or off under the Geometry section.

SET INVISGEOM QUERY – Shows the current status for SET INVISGEOM in the status bar.

You can remove features by typing ocsetup /uninstall DHCPServerCore

To see a list of features that have been installed type oclist. The table below shows all of the possible features that can be installed.